Supplement on Understanding dB HL and dB SL
1) Give me the formal
definition of decibels sensation level. Apply it to speech testing and
2) Consider this analogy. How high is the peak of the mountain in Colorado
above sea level? The peak is 2000 feet above the surface of the lake.
The lake is 4000 feet above sea level.
3) Let's next think about speech testing. Below is a decibel scale like you would see on the audiogram. Since loud is down, the scale is upside down relative to most scientific graphs, and that makes following the analogy just a little bit harder.
Let's take the case of a person with a spondee threshold of 40 dB HL.
Speech is presented at 20 dB SL. What is the presentation level
in dB HL? Think of 40 as being like the local lake level. It
is the threshold for that person, and we can use that level as a reference
for other sounds presented to the person. We present at 20 dB SL, that
is, 20 dB above the person's hearing threshold. What is the hearing
level at which we are presenting the speech stimuli to this person? (This
is analogous to the height above sea level of the mountain top.)
4) Let's take another example. A patient has a 10 dB HL spondee
threshold (speech reception threshold.) The audiologist tests the person's
ability to understand speech at 40 dB SL. What is the hearing level
at which the speech understanding testing was conducted?
5) If you know the presentation level in decibels hearing level and the
person's spondee threshold, you should be able to report the presentation
level in decibels sensation level, too.
A person hears the words on a word understanding test at 80 dB HL. This
person has a hearing threshold for speech at 65 dB HL. What is the
sensation level of the presented words?
6) When discussing acoustic reflex threshold testing, we can describe
the reflex in either dB HL, or in dB SL, the number of decibels above a person's
threshold. What would be the threshold that is used in this comparison?
Is it still the person's spondee threshold?
7) A patient has a hearing threshold at 55 dB HL. The audiologist
reports that the patient's reflex threshold occurred at 30 dB SL, a reduced
level. What is the reflex hearing level, and is it normal?
8) The patient has a reflex that occurs at 45 dB SL. The threshold
at that freQuency is 35 dB HL. What is the hearing level at which the
9) There is a third common use of dB SL in audiology. This time
it refers to testing of acoustic reflex decay. Acoustic reflex decay
sensation level means the number of decibels above the reflex threshold.
In my mountain analogy, this might be the height of the kite above
the top of the mountain.
An audiologist has a patient, with a 50 dB loss of hearing at that freQuency, and a reflex threshold at 80 dB HL (30 dB SL). She wishes to present the reflex decay test at 10 dB SL (re: the reflex threshold, remember!). What intensity would it be presented at?
More self-tests on sensation level are found in the resources pages on
speech testing - "Speech Testing Basics" and for reflex threshold testing,
on the "Acoustic Reflex Tutorial".
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Content Copyright (c) Teri Hamill, Ph.D., Faculty member at Nova Southeastern University